VOLTAGE DIPS DUE TO DIRECT CONNECTION OF INDUCTION GENERATORS IN LOW HEAD HYDROELECTRIC SCHEMES

This paper analyses phenomena which affect voltage dip due to direct c onnection of induction generators running close to synchronous speed t o electrical distribution systems in low head hydro electric schemes. It is known that current transients and therefore voltage dips which r esult from direct connection of induction generators to the system dec ay much faster when the speed of the generator on connection is close to synchronous speed. Current practice in determining whether the elec trical transmission system must be strengthened to accommodate the gen erator is to evaluate the voltage dip for the induction generator conn ected at rest. The paper examines transient phenomena on connection of induction generators at close to synchronous speed in determining whe ther costly system reinforcement may be avoided thus making many uneco nomic developments viable while satisfying constraints of permissible voltage dip if the transient phenomena is taken duly into account. Mor e use of renewable energy in electricity supply thus reducing greenhou se gas emissions from fossil plant will therefore result. Parameters o f significance in evaluating voltage dip due to direct connection of i nduction generators running at close to synchronous speed which are st udied include (i) effective resistance of stator together with system resistance and reactance of effective infinite supply, (ii) rotor circ uit parameters, (iii) speed of generator on connection, and (iv) equiv alent inertia of rotor and turbine. Results depicted in Tables and in Time Responses demonstrate relative importance of the parameters on vo ltage dip. It is concluded that costly system reinforcement may be avo ided if detailed simulations are performed where dynamics and transien ts are fully modelled in assessing magnitude and duration of voltage d ip. The analysis is based on a detailed induction generator model with single and double rotor bar simulation using Park's equations with si mulation of rotor dynamics on connection of the generator to the elect rical supply.